Software Drives OEM Toward Efficiency and Energy Savings

ABB designed software for its ACS800 drive so Curtis-Toledo could improve the operation of its rotary-screw compressors. The customized software can control the system pressure, air delivery, oil temperature and duty cycle directly from the drive.

By John Wilmes, ABB Inc.

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The drive software indicates when to service all of the components that need to be changed periodically, including oil, separator elements, oil filter, drive enclosure filter and air filter. Adjustable maintenance timers count down until they reach zero; an alarm is then displayed on the touch screen indicating which maintenance function needs attention. Once the issue has been addressed, the operator resets the timer, which then starts counting down again.

At the request of Curtis-Toledo, the control system also provides automatic lead/lag control for two machines: When one machine can’t keep up with demand, it starts the secondary machine automatically. Conversely, the secondary machine is taken off line when not needed, eliminating the need for any external device.

The ACS800 drive has a fault history log to help the operator troubleshoot problems. If the machine faults, an alarm is activated and a window pops up on the touch screen. The display tells the operator what the fault is and how to correct it.

Warnings and faults displayed in the fault/warning history include:
• E-stop: a safety circuit required by OSHA. In case of a plant emergency, a push button on the machine immediately shuts down the drive;
• Remote start/stop: a hard-wired push button that can start or stop the machine from a remote location. This is a convenient when an operator cannot get to the touch screen;
• Input air block detection: This safety measure shuts down the machine if the airflow is blocked; and
• Motor temperature protection: This safety circuit will shut down the machine in case of extreme overheating.

The ACS800 drive has a feature called Direct Torque Control (DTC), which provides fast, accurate control of both motor speed and torque without pulse encoder feedback from the motor shaft. This enables the drive to calculate the torque and flux of the motor 40,000 times per second and makes the motor controllers tripless, which can minimize down time due to random faults.

A unique feature on the Curtis-Toledo installation is the addition of a secondary drive in the machine to cool the oil. “We found through testing that if the speed varied on the main compressor drive, and the cooler ran at a constant speed, the oil would overcool and moisture would build up, resulting in a machine breakdown,” says Boren. “What we’ve done is put another ABB drive (the ACS550 series) on the fan motor. We take the discharge oil temperature and run a PID loop on temperature, meaning that the speed of the cooler fan varies so that the oil temperature is maintained.”

Better temperature control can result in longer oil life since the oil won’t breakdown if its temperature is regulated and controlled within safe limits. Controlling the temperature also removes moisture from the oil, thereby eliminating a major cause of mechanical breakdowns.

The fan drive is also integrated into the software so the operator can use the touch screen to monitor its current, torque, voltage, power, temperature feedback and temperature set point.

John Wilmes is district manager for ABB Low Voltage Products. He works closely with manufacturers to provide automation products and solutions to electrical distributors and end users. E-mail him at

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